High speed steel having high wear resistance

ABSTRACT

A high speed steel having high wear resistance consisting essentially of 3.1 to 6.3% by weight of carbon, 5 to 12% by weight of vanadium, 3 to 10% by weight of niobium, and the balance substantially iron, wherein all of vanadium and niobium reacts with carbon, 1.4 to 3.6% by weight of carbon forms cementite and 0.1 to 0.6% by weight of carbon dissolves in a ferrous matrix as hardened.

United States Patent Akahori et a1.

HIGH SPEED STEEL HAVING HIGH WEAR RESISTANCE inventors: KimihikoAkahori, Katsuta;

Masayuki Era, Hitachi, both of Japan Assignee: Hitachi, Ltd., JapanFiled: Jan. 23, 1974 Appl. No.: 435,952

Foreign Application Priority Data Jan. 24, 1973. Japan 48-9543 US. Cl148/31; 75/123 J; 75/126 A; 75/126 E; 75/126 F; 75/128 D Int. Cl. C22C38/12; C22C 38/36 Field of Search 75/123 R, 123 J, 126 A, 75/128 D, 12813,128 V; 148/31 References Cited UNITED STATES PATENTS 11/1951 Giles75/126 A OTHER PUBLICATIONS Tool Steels, Roberts et al., 1962, pp.521-524.

Primary Examiner-C. Lovell Attorney, Agent, or Firm-Craig & Antonelli [57] ABSTRACT A high speed steel having high wear resistance consistingessentially of 3.1 to 6.3% by weight of carbon, 5 to 12% by weight ofvanadium, 3 to 10% by weight of niobium, and the balance substantiallyiron, wherein all of vanadium and niobium reacts with carbon, 1.4 to

I 3.6% by weight of carbon forms cementite and 0.1 to

0.6% by weightof carbon dissolves in a ferrous matrix as hardened.

11 Claims, 8 Drawing Figures US. Patent ABRASION QUANTITY (9) Dec. 30,1975 Sheet10f4 3,929,518

FIG. I

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6 @8755: wmxoom IICD HARDENING TEMPERATURE (C) FIG.8

TEMPERING TEMPERATURE HIGHSPEED STEEL HAVING HIGH WEAR RESISTANCEBACKGROUND OF THE INVENTION 1. Field of the Invention r This inventionrelates to a high speed steel having high wear resistance, and moreparticularly to a high speed steel, wherein carbides of vanadium andniobium and cementite (Fe C) are crystallized in a ferrous matrix.

2. Description of the Prior Art The wear resistance of a steel, ingeneral, increases with the increase in the amount of MC type carbides.It is accordingly a common practice to add to a steel elements whichform MC type carbides, for improving wear resistance. However, theincrease in the amount of the elements which form MC type carbides,gives rise to a problemassociated with a melting operation, with theresultant difficulties in production of steels, or it may be evenimpossible to produce such a steel. Among typical high speed steelswhich have improved wear resistance due to the presence of MC typecarbides, there is a steel which contains vanadium as acarbide formingelement. This high speed steel essentially contains Fe and has VCdispersed in the ferrous matrix containing a carbon solid solutiontherein. In the interest of facilitating heat treatment, this type ofhigh speed steel contains Cr,.Ni or the like, or the elements such asMn, Si or the like remaining therein which is added for the purpose ofremoving adverse elements such as oxygen. The amount of vanadium to beadded is such that the entire amount thereof combines with C to form VC.Furthermore, the amount of carbon is such as exceeding the amountrequired for the formation of VC, in an attempt to assist in hardeningof matrix. However, such a high speed steel has tobe encountered withdifficulties in melting, in the case of the amount of vanadium exceeding7% by weight, which forms carbide. This is because, in the melting of ahigh speed steel containing VC which is dispersed in a ferrous matrix,vanadium of an amount exceeding a certain level follows a different typeof crystallization which accompanies local aggregation of VC. Morespecifically, VC crystallizes as eutectic crystals in a case where V isnot more than 7% by weight, while in the case of V of an amountexceeding 7% by weight, the part of V exceeding said 7% crystallizes asprimary crystals. The density of VC is as low as 5.6 g/cm, as comparedwith the density of iron of 7.87 g/cm. However, VC crystallized aseutectic crystalls has a narrow solidifying temperature range, such thatmost of VC will not float to the top surface of a melt and thus remainssolidified therein in a manner to disperse in an ingot uniformly,thereby presenting high wear resistance. In addition, the crystal grainsthereof are substantially fine, thus presenting high mechanicalstrength. In contrast thereto, VC crystallizing as pri- 2 parts of theingot, thus failing to present uniform wear resistance and mechanicalstrength throughout the ingot. For such reasons, it"has been consideredthat the content of-V of no less than 7% by weight gives harm to highspeed steels.

As has been described, the wear resistance of a high speed steelprimarily depends on the amount of MC type carbides formed, and the wearresistance increases with, the increase'in the amount of carbides. Itfollows that the ,utility of the high speed steel will be even highlyevaluated, if an increased amount of VC is dispersed in an ingot and yetthe crystal grains of VC which crystalizes as primary crystals arerendered finer. Meanwhile, the aforesaid high speed steel finds itsapplication as a Sendzimir work roll which is principally used forrolling a bright annealed stainless strip. On the other hand, alimitation as to the length is imposed on a'stri'p which is rolled bythe high speed steel Sendzimir work rolls without its brightness beingimpaired. In other words, the length of a rolled strip having uniformbrightness is limited up to 750 m, and in case the strip is longer thanthat, then the rolls'catch on their surfaces the strip powder producedduring the rolling operation, thereby causing roughened surfaces in astrip due to seizure of powder to roll surfaces. The inventorsdiscovered that such surface roughening phenomenon may be improved withthe increase in amount of carmary crystals has a wide solidifyingtemperature range,

bides formed.

As is already clear, the improvement in wear resistance of a high speedsteel dictates the distribution of a relatively great amount of MC typecarbides, and in addition, the achievement of long lasting capability ofthe rolls of such high speed steel to present good surface condition forthe rolled strip requires uniform distribution of a relatively greatamount of carbides in an ingot.

Under such circumstances, the inventors first examined the possibilityof uniform distribution in an ingot, of VC which crystallizes as primarycrystals. To this end, the inventors added elements which formed solidsolutions with VC, whereby the density of the carbides is increased.Included by the elements which form solid solutions with VC are Ti, Nband Ta.'Those elements form carbides of MC type by combining with orbonding to carbon, such that they can not'only prevent the Moreparticularly, the-density of the titanium carbide is as low as 4.9 g/cm,as compared with that of vanadium carbide, thereby failing-to preventvanadium carbide from floating in a melt. On the other hand, the densityof carbide of tantalum is too great to cause the resultant solidsolution of vanadium carbide and tantalum to sink to the lower part ofan ingot. In contrast to this, the density of the carbide of niobium is7.8 g/cm which approximates that of iron, such that the carbide ofvanadium forming a solid solution with niobium gives a danger ofneitherfloating nor sinking in a melt. Thus, niobium has proved to beeffective for preventing the floating of vanadium carbide. The continuedexperiment, however, further reveals that carbide'of vanadium forming asolid solution with niobiumv crystallizes at a temperature higher thanthat of the crystallization of vanadium carbide, and as a result, theaddition of niobium presents a greater amount of carbide, as comparedwith the mereaddition of vanadium.

In view that niobium forms carbide and the crystallization temperatureis higher than that of vanadium, the addition of niobium alone was alsotried. However, the primary crystals of NbC gave a large grain size,with the attendant extremely lowered toughness.

Under such circumstances, there has come to the fore the development ofahigh speed steel which prevents the primary crystals of VC fromfloating, due to the addition of Nb, and which contains as great amountcrystallized as ternary-component eutectic crystals consistingof'carbides of vanadium and niobium, 'yFe of carbides of the primarycrystals of VC and Nb as a possible, as far as such carbides ;arepresent in the form of fine particles.

SUMMARY or THE INVENTION Object-of the Invention It is accordinglyanobject of the invention to provide a novel high speed steel, in whichthe primary crystals of VC are uniformly dispersed throughout an ingotand which fine particles of carbides otherrthan VC are present in agreat amount. v 7

It is another object of the invention to provide a high speedsteel whichpermits the secondary hardening due to hardening andtempering g Itis afurther object of the invention to provide ahigh speed steel which maybe used for Sendzimir workrolls for rolling a bright annealed stainlessstrip and assures the capability to maintain a smooth surface conditionin rolling stripsfor a period of time twice that of the conventionalrolls of this type.

r Statement of the Invention According to the present invention, thereis provided a high speed'steel having high wear resistance, consistingessentially of 3.1 to 6.3% by weight of carbon, to 1.2% by weight ofvanadium, 3 to 10% by weight of niobium, and the balance substantiallyiron, wherein all of ,vanadium and niobium reacts with carbon, 1.4 to 3.6% by weight of carbon forms cementite and 0.1 to 0.6% by weight ofcarbon dissolves in a ferrous matrix ashardened.

The present invention is based on discoveries that an ingot ofia highspeed steel may be produced by melting, in-which ingot there areuniformly dispersed carbides of vanadium and niobium, if 5 to 12% byweight of vanadium and 3 to 1.0% by weight of niobium are coexistent forforming carbides with carbon. More particularly, the present inventioncontemplates to present a relatively great amount of carbides of niobiumand vanadium, thereby improving wear resistance and the capability ofpresenting good surface condition for a rolled strip for long period oftime, when used as a roll, whiledesired mechanical strength is retained.

The highspeed steel of the present invention contains not only carbidesof vanadium and niobium but also cementite (Fe c) of 1.4 to 3.6% byweightwhich consists of carbon and. iron, in a uniformly dispersedmanner in an ingot. The grain size of the cementite (Fe,C) is extremelyfine, whereby even if the amount of carbides is increased, there willresult no appreciable decrease in mechanical strength. lt-is known inthe field of various types of cast iron thatthe formation of Fe Cimproves the wear resistance of a steel. However, in the conventionalcast iron, Fe; C ispresent in the form of binary-component eutecticcrystals, having an ex-' and Fe C, and thus Fe C appearing as suchternarycomponent eutectic crystals is prevented from its grain growthdue to the presence of vanadium and niobium, with the result that itremains'uniformly in a steel, with the grain size thereof beingmaintained in the form of fine particles. The reason why the grain sizeof Fe C crystals is fine is that the formation of carbides of vanadiumand niobium takes place prior to the formation of Fe' -,C, and this facthas been discovered by the inventors.

With the melting production of a high speed steel according to thepresent invention, carbides consisting essentially ofrNb crystallizesinthe form that they dissolves asmall amount of vanadium therein. Then,carbides consisting essentially of vanadium will crystallize in the formthat they dissolves asmall amount of niobiumtherein, followed bycrystallization of Fe c. The carbide consisting essentially of vanadiumand dissolving a small amount of niobiumtherein is lessin density thanthat of matrix, and hence it tends to float in a melt. However, thefloating of such carbides are prevented by the carbides consistingessentially of niobium which has crystallized beforehand,such that theaforesaid carbides willbe uniformly dispersed in a matrix. The'portionof the melt, from which the carbides have crystallized, remains in theform of 'yFe, which in turn is precipitated as aFe and Fe C in thecourse of cooling. After solidification, ingot is heated for hardeningmatrix to an austenizing temperature,-followed by quenching to give thematrix of a martensite structure.

However, in the course of heating, Fe Cwhich has been precipitated from:yFe is decomposed to be dissolved in 'yFe again. The amount of carbonwhich has been decomposed from Fe' C- and dissolved into 'yFe increaseswith the increase in heating temperature.

Besthardening may be achieved, if the high speed steel of .the inventionis heated to a temperature of 800 to 1,000C, preferably 900C, followedby hardening. The

amount of carbon dissolved into 'yFe, in this state, is 0.1

to 0.6% by weight. After hardening, the ductility of matrix of amartensite is raised by tempering. However, the hardnessof a high speedsteel islowered by this tempering treatment, such that the temperingtemperature should be-below 200C, preferably in the neighborhood. of C.

The content of vanadium according to a high speed steel of the inventionshould range from 5 to 12% by weight. The vanadium in this range formsVC, presenting hi'gh wear resistance. Vanadium of an amount of lessthan.5% by weight fails to presentdesired wear resistance. i

The formation of Fe C of a great amount leads to extremely loweredtoughness. On the other hand, vanadium of an amount more than 12% byweight fails to prevent the floating of the primary crystals of carbidesconsisting essentially of vanadium, while most of niobium formscarbides. Although niobium is added for the dual purposes of increasingthe amount of carbides and preventing the floating of the primarycrystals of VC, it also serves to prevent the decrease in toughness of asteel by presentingternary-component eutectic crystals of a fine grainsize. If niobium is no more than 3% by weight in amounts, niobium willnot crystallize as the primary crystals, thus failing to preventfloating of VC. In case niobium is more than 10% by weight'in amounts,the grain size ofv the primary crystals of carbides consistingessentially of niobium is increased, thereby lowering the toughness of asteel. There is present an optimum ratio, in amount, of vanadium toniobium. According to experiments, the optimum ratio Nb wt% V wt% 0.5 to1.0. Thus, as far as the ratio is maintained in this range, the primarycarbide crystals will not grow, but will be dispersed in the matrixuniformly.

The weight ratio of Nb to V of no more than 0.5 still presents carbidesof a finer grain size, while presenting a tendency of floating of theprimary carbide crystals in a melt. On the other hand, if the ratio isno less than 1 then the grain size of the primary carbide crystals willbecome larger.

Carbon is added for the dual reasons, i.e., for forming carbides and forhardening matirx. For formation of VC containing l% by weight ofvanadium, the addition of 0.24% by weight of carbon is required, whilefor the formation of NbC containing 1% by weight of niobium, theaddition of 0.13% by weight of carbon is required. It follows then thatfor bonding carbon to the entire amount of vanadium and niobium, theaddition of 1.6 to 4.2% by weight of carbon is required in total.Meanwhile, according to the present invention, the amount of cabides maybe increased without impairing the mechanical strength of a steel bycrystallizing eutectic crystals, Fe C, in a fine grain form. In thisrespect, the eutectic crystals, Fe C, should crystallize asternarycomponent eutectic crystals, and for this purpose, carbon of anamount of no less than 1.4% is required. The area ratio of Fe;, C thusobtained is 20%. On the other hand, the amount of Fe C should be limitedto a certain level, because if the amount of Fe C is excessive, thebrittleness of a steel will increase, even if Fe C is present in theform of a fine grain size. Specifically, the amount of Fe C should bemaintained below 50% in terms of area ratio. For this reason, the amountof carbon required for the formation of Fe C should be below 3.6% byweight, inclusive. Accordingly, the total amount of carbon required forformation of carbides will be 3.0 to 7.8% by weight. On the other hand,since 0.1 to 0.6% by weight of carbon is dissolved in a ferrous matrixin a hardened condition, the total amount of carbon required will befurther increased. However, if the amount of carbon is excessive andhence the excessive amount of carbides is formed, then there will resultdifficulties with the melting operation, such that an ordinary type highfrequency induction furnace no longer finds its application in meltingsuch materials. Experiments reveal that for heating and meltingaccording to a high frequency induction furnace, the amount of carbonshould be no more than 6.3% by weight. The carbides of vanadium of 5 to12% by weight occupies 8.2 to 19.7% in terms of area ratio, while thecarbides of niobium of 3 to by weight occupies about 3.4 to l 1.4% interms of area ratio. As the amount of MC type carbides increases, thewear resistance of a steel increases, and as a result, the excellentwear resistance may be obtained at an area ratio of over 15%. On theother hand, in case the area ratio of Fe C is over and yet in case thesum of the area ratio of Fe C and that of the aforesaid MC type carbidesis over then the capability of maintaining good surface condition of astrip will be materially enhanced.

The high speed steel according to the present invention may contain Mn,Si, P and S as impurities. The

amounts ofMn and Si of below 2% by weight, respectively, are allowable,because they serve as deoxidizers, while the amounts of P and S of below0.020% by weight, respectively, are allowable. Furthermore, the highspeed steel of the invention may contain Ni, Cr, Mo, W and Co, forimproving hardenability and tempering resistance. The content of Nishould be no more than 2% by weight, Crshould range from 2 to 6% byweight, Mo from 1 to 6% by weight, W from 1 to 6% by weight and Co below10% by weight. The aforesaid ranges of these elements are based on thefollowing:

Nickel may dissolve into a matrix to improve the harnenability of asteel. However, Ni of an amount of over 2% by weight softens the matrix.Chromium may dissolve in a matrix upon hardening treatment to improvehardenability, but loses such effect, unless the amount thereof exceeds2% by weight. If the amount of chromium exceeds 6% by weight, itpresents a large grain size of casting structure. Part of molybdenumdissolves into a matrix to better hardenability, while enhancing thesecondary hardening characteristic due to tempering, and temperingresistance. For this purpose, the amount of molybdenum should be no lessthan 1% by weight. Molybdenum of an amount exceeding 6% by weight lowerstoughness. Tungsten serves a function similar to that of molybdenum,such that it may be used in place of molybdenum. The amount of tungstento be added is likewise from 1 to 6% by weight. The only difference oftungstenfrom molybdenum is that the former widens an optimum hardeningand tempering temperature ranges. Accordingly, the both elements shouldbe combines in the practical application. Cobalt enhances the temperingresistance, and it should be contained in an amount of below 10% byweight. The further continued experiments made by the inventors revealthe advantage of the combined use of three types of elements of Cr, Moand W asalloy elements. More specifically, when the aforesaid threetypes of elements are contained in a high speed steel of the inventionin the aforesaid ranges, there will be achieved the secondary hardening,when tempered at a temperature of 450 to 550C. Another discovery isthat, upon rolling of a bright annealed stainless strip by usingSendzimir work rolls, the carbides of an area ratio of over 35% maypresent the capability of maintaining smooth surface condition for aperiod of time twice that of the conventional roll.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a graph showing wear amountsof high speed steel samples used for wear tests according to experimentsof the invention;

FIG. 2 is a graph showing rupture loads measured in bending tests;

FIG. 3 is a plot illustrating the relationship of hardness and hardeningtemperature for high speed steel samples;

FIG 4 is a plot showing the relationship of hardness and temperingtemperature;

FIG. 5 is a graph showing rupture loads measured in bending tests forhigh speed steel samples according to another type of embodiment;

FIG. 6 is a graph showing results of wear tests;

FIG. 7 is a plot showing the relationship of hardness and hardeningtemperature; and

FIG. 8 is a plot showing the relationship of hardness and temperingtemperature.

' EXAMPLES Table 1 shows chemical compositions of high speed steels usedin the various experiments of the invention, coupled with area ratios ofcarbides calculatedv from the aforesaid chemical compositions plushardness obtained when subjected to hardening treatment including oilquenching from 900C, followed by-tempering at 150C. Among samples, No. 1designates a conventional high speed steel, Nos. 2 and 3 and Nos. and 11 represent those presented for comparison purpose with samples ofsteels of the invention, and Nos. 4 to 9 represent high speed steelsaccording to the present invention. Those steels were prepared bymelting in air atmosphere in a high frequency induction furnace, afterwhich'they were cast in metallic molds having 60 mm d). Then, varioussamples were cut from the center portions of ingots, respectively.

In passing, the amounts of P and S fall in a range from 0.010 to 0.020%byweight, respectively.

Table 1 Chemical composition (wt%) Area ratio of carbide wear resistanceand mechanical strength, but suffered from a danger of causing surfaceroughness, because of smaller area ratio of Fe C. The relationship oftemperature to hardness in hardening treatment was obtained as to Nos.5, 8 and 10. FIG. 3 shows the results thereof, presenting Rockwellhardness (I-I C) as an ordinate and hardening temperature as abscissa.In either sample, a high hardness was obtained at the hardeningtemperature of 800 to 1,000C. Particularly, there was obtained thehighest hardness at 900C. FIG. 4 shows the relationship of the temperingtemperature to hardness, by using samples'which were tempered, after oilquenching from a temperature of 900C. In either sample, the hardnessdecreases with the increase in tempering temperature.

As has been described earlier, the-addition of an element selected fromCr, Mo, W, Co and Ni to the high speed steel of the invention presentsbetter hardenability. The effect of the elements added is particularlyprominent, when Cr, Mo and W are added in Hardness after Special typeheat treatment No. C Si Mn V Nb carbide Fe,C Total (H C) 1 3.98 0.170.63 6.34 10 32 42 67.0 2 4.89 0.16 0.71 2.83 5.67 11 47 58 67.5 3 3.570.20 0.55 7.50 5.78 18 10 28 67.5 4 3.65 0.19 0.58 5.04 5.12 l4 22 37 I67.0 5 5.07 0.19 0.50 5.25 5.31 15 42 57 68.0 6 4.67 0.19 0.74 7.32 5.4118 28 46 68.0 7 5.48 0.17 0.70 7.31 5.75 19 39 58 69.0 8 .4.74 0.20'0.64 9.51 5.39 22 21 43 70.0 9 5.81 0.l8 0.61 9.65 9.26 26 29 70.5 105.27 0.19 s 0.70 10.58 9.00 28 17 45 70.5 11 4.40 0.18 0.68 11.34 8.9429 3 32 69.0

combination. This .presents thesecondary hardening due to temperingtreatment. For thistest, high speed steel samples having compositions asshown in FIG. 2 were prepared in the same manner as has been described,and tested for rupture loads in bending tests and wear amounts and forthe relationship of hardening and tempering temperature to, hardness. Inpassing, the amountsof S and P in the respective sample ranged from0.010 to 0.020% by weight,.respectively.

Table 2 Area Chemical composition (wt%) ratio of v entire carbides No.Mn Cr Mo Nb lent wear resistance. This test reveals that the wearresistance increases with the increase in the area ratio of MC typecarbides which consist of V, Nb and C.

This test was then followed by bending tests for measuringru'ptureloads. The bending test was carried out by placing bar shapedsamples of 2 mm X 22 mm on tools spaced 12 mm apart from each other.Then, loads were applied from above on the bar shaped samples forbending same until they were broken. FIG. 2 shows rupture loads of thesamples used. The high speed steels according to the present inventionpresented high rupture loads, despite a greater total amount ofcarbides, presenting excellent high wear resistance and mechanicalstrength. Nos. 10 and 11 showed excellent FIG. 5 shows rupture loadsobtained in bending tests which were carried out in the same manner ashas been described. The rupture loads were increased by about 30 lcg/mmdue to the addition of Cr, Mo, W. These values are apparently higherthan any one of values given in Table 1. FIG. 6 shows the wear amountsobtained in the wear tests, while FIG. 7 shows the rela-.

optimum hardening temperature is proved to be in the range from 800 to1,000C, preferably 900C. FIG. 8 shows the relationship of temperingtemperature to hardness of the samples which were subjected to temperingafter oil quenching from 1,000C. It should be noted by referring to FIG.8 that there takes place the secondary hardening by using tempering at450 to 550C.

As is apparent from the foregoing description, the high speed steelsaccording to the present invention present extremely high wearresistance and excellent mechanical strength.

The high speed steels according to the present invention are adapted foruse in a Sendzimir work rolls for rolling bright annealed stainlessstrip. In this respect, the length of strip which can be continuouslyrolled without causing surface roughness was"1,500 m. This valuecorresponds to about twice the length of conventional high speed steelcontaining less than 7% by weight of vanadium.

We claim:

1. A high speed steel having high wear resistance consisting essentiallyof 3.1 to 6.3% by weight of carbon, to 12% by weight of vanadium, 3 to10% by weight of niobium, and the balance essentially iron, wherein allof vanadium and niobium is combined with carbon, 1.4 to 3.6% by weightof carbon forms cementite in the form of ternary-component eutecticcrystals of carbides of vanadium and niobium, 'yFe and Fe C and 0.1 to0.6% by weight of carbon is dissolved in a ferrous matrix as hardenedand wherein the weight ratio of niobium to vanadium is from 0.5 to 1.

2. A high speed steel according to claim 1, wherein the area ratio ofcarbides of vanadium and niobium and cementite is more than 35%.

3. A high speed steel according to claim 1, wherein said ferrous matrixis a martensite matrix.

4. A high speed steel according to claim 3, wherein the area ratio ofcarbides of vanadium and niobium and cementite is more than 35%.

5. A high speed steel which consists essentially of 3.1 to 6.3% byweight of carbon, 5 to 12% by weight of vanadium, 3 to 10% by weight ofniobium, 2 to 6% by weight of chromium, 1 to 6% by weight of molybde'num, l to 6% by weight of tungsten, and the balance essentially iron,substantially all of vanadium and niobium being combined with carbon,1.4 to 3.6% by weight of carbon forming cementite in the form of ternary-component eutectic crystals of carbides of vanadium and niobium, 'yFeand Fe C and 0.1 to 0.6% by weight of carbon being dissolved in aferrous matrix as hardened and wherein the weight ratio of niobium tovanadium is from 0.5 to l.

6. A high speed steel according to claim 5, wherein the area ratio ofcarbides of vanadium and niobium and cementite is more than 35%.

7. A high speed steel according to claim 5, wherein said ferrous matrixis a martensite matrix.

8. A high speed steel consisting essentially of 3.1 to 6.3% by weight ofcarbon, 5 to 12% by weight of vanadium, 3 to 10% by weight of niobium,up to 2% by weight of silicon, up to 2% by weight of manganese, and thebalance essentially iron, wherein all of vanadium and niobium iscombined with carbon, 1.4 to 3.6% by weight of carbon forms cementite inthe form of ternary -component eutectic crystals of carbides of vanadiumand niobium, 'yFe and Fe C and 0.1 to 0.6% by weight of carbon isdissolved in a ferrous matrix as hardened and wherein the weight ratioof niobium to vanadium is from 0.5 to 1.

9. A high speed steel according to claim 8, wherein said ferrous matrixis a martensite matrix.

10. A high speed steel consisting essentially of 3.1 to 6.3% by weightofcarbon, 5 to 12% by weight of vanadium, 3 to 10% by weight of niobium,up to 2% by weight of nickel, 2 to 6% by weight of chromium, 1 to 6% byweight of molybdenum, l to 6% by weight of tungsten, up to 10% by weightof cobalt, up to 2% by weight of silicon, up to 2% by weight ofmanganese, and tha balance essentially iron, wherein all of vanadium andniobium'is combined with carbon, 1.4 to 3.6% by weight of carbon formscementite in the form of ternary-component eutectic crystals of carbidesof vanadium and niobium, 71% and Fe C and 0.1 to 0.6% by weight ofcarbon is dissolved in a ferrous matrix as hardened and wherein theweight ratio of niobium to vanadium is from0.5 to l.

l l. A high speed steel according to claim 10, wherein said ferrousm'atrix'is a martensite matrix.

1. A HIGH SPEED STEEL HAVING HIGH WEAR RESISTANCE CONSISTING ESSENTIALLYOF 3.1 TO 6.3% BY WEIGHT OF CARBON, 5 TO 12% BY WEIGHT OF VANADIUM, 3 TO10% BY WEIGHT OF NIOBIUM, AND THE BALANCE ESSENTIALLY IRON, WHEREIN ALLOF VANADIUM AND NIOBIUM IS COMBINED WITH CARBON, 1.4 TO 3.6% BY WEIGHTOF CARBON FORMS CEMENTITE IN THE FORM OF TERNARY-COMPONENT EUTECTICCRYSTALS OF CARBIDES OF VANADIUM AND NIOBIUM, YFE AND FE3C AND 0.1 TO0.6% BY WEIGHT OF CARBON IS DISSOLVED IN A FERROUS MATRIX AS HARDENEDAND WHEREIN THE WEIGHT RATIO OF NIOBIUM TO VANADIUM IS FROM 0.5 TO
 1. 2.A high speed steel according to claim 1, wherein the area ratio ofcarbides of vanadium and niobium and cementite is more than 35%.
 3. Ahigh speed steel according to claim 1, wherein said ferrous matrix is amartensite matrix.
 4. A high speed steel according to claim 3, whereinthe area ratio of carbides of vanadium and niobium and cementite is morethan 35%.
 5. A high speed steel which consists essentially of 3.1 to6.3% by weight of carbon, 5 to 12% by weight of vanadium, 3 to 10% byweight of niobium, 2 to 6% by weight of chromium, 1 to 6% by weight ofmolybdenum, 1 to 6% by weight of tungsten, and the balance essentiallyiron, substantially all of vanadium and niobium being combined withcarbon, 1.4 to 3.6% by weight of carbon forming cementite in the form ofternary -component eutectic crystals of carbides of vanadium andniobium, gamma Fe and Fe3C and 0.1 to 0.6% by weight of carbon beingdissolved in a ferrous matrix as hardened and wherein the weight ratioof niobium to vanadium is from 0.5 to
 1. 6. A high speed steel accordingto claim 5, wherein the area ratio of carbides of vanadium and niobiumand cementite is more than 35%.
 7. A high speed steel according to claim5, wherein saiD ferrous matrix is a martensite matrix.
 8. A high speedsteel consisting essentially of 3.1 to 6.3% by weight of carbon, 5 to12% by weight of vanadium, 3 to 10% by weight of niobium, up to 2% byweight of silicon, up to 2% by weight of manganese, and the balanceessentially iron, wherein all of vanadium and niobium is combined withcarbon, 1.4 to 3.6% by weight of carbon forms cementite in the form ofternary -component eutectic crystals of carbides of vanadium andniobium, gamma Fe and Fe3C and 0.1 to 0.6% by weight of carbon isdissolved in a ferrous matrix as hardened and wherein the weight ratioof niobium to vanadium is from 0.5 to
 1. 9. A high speed steel accordingto claim 8, wherein said ferrous matrix is a martensite matrix.
 10. Ahigh speed steel consisting essentially of 3.1 to 6.3% by weight ofcarbon, 5 to 12% by weight of vanadium, 3 to 10% by weight of niobium,up to 2% by weight of nickel, 2 to 6% by weight of chromium, 1 to 6% byweight of molybdenum, 1 to 6% by weight of tungsten, up to 10% by weightof cobalt, up to 2% by weight of silicon, up to 2% by weight ofmanganese, and tha balance essentially iron, wherein all of vanadium andniobium is combined with carbon, 1.4 to 3.6% by weight of carbon formscementite in the form of ternary-component eutectic crystals of carbidesof vanadium and niobium, gamma Fe and Fe3C and 0.1 to 0.6% by weight ofcarbon is dissolved in a ferrous matrix as hardened and wherein theweight ratio of niobium to vanadium is from 0.5 to
 1. 11. A high speedsteel according to claim 10, wherein said ferrous matrix is a martensitematrix.